Read How a brand of chalk achieved cult status among mathematicians (CNN)
Hagoromo chalk has developed a cult following among mathematicians. When the company went out of business, chaos ensued.
I’ve read this same sort of article in other venues in the past, but closer to the revival of the company. This seems to have cropped up again because the original owner of the Japanese company has passed away in the last month.

👓 Why this Japanese chalk is being hoarded by mathematicians | Boing Boing

Watched Why this Japanese chalk is being hoarded by mathematicians by Mark Frauenfelder from Boing Boing

Hagoromo Fulltouch Chalk is highly coveted around the world by mathematicians, who say it's superior to other kinds of chalk because it has an almost buttery texture and erases easily. When Hagoromo announced it was ceasing production, many mathematicians bought lifetime supplies, like one professor who has a four-stick-a-day habit. But a Korean company bought Hagoromo and has faithfully reproduced the original recipe so there is no longer a need to stockpile it. It's sometimes available on Amazon from third-party resellers.